This application relates to the use of heat shock proteins and similar peptide-binding proteins to stimulate an immunological response against antigens, including cancer-related antigens, autoimmune antigens and infectious disease antigens, found in a mammalian host.
Heat shock proteins were originally observed to be expressed in increased amounts in mammalian cells which were exposed to sudden elevations of temperature, while the expression of most cellular proteins is significantly reduced. It has since been determined that such proteins are produced in response to various types of stress, including glucose deprivation. As used herein, the term "heat shock protein" will be used to encompass both proteins that are expressly labeled as such as well as other stress proteins, including homologs of such proteins that are expressed constitutively (i.e., in the absence of stressful conditions). Examples of heat shock proteins include BiP (also referred to as grp78), hsp/hsc70, gp96 (grp94), hsp60, hsp40 and hsp90.
Heat shock proteins have the ability to bind other proteins in their non-native states, and in particular to bind nascent proteins emerging from the ribosomes or extruded into endoplasmic reticulum. Hendrick and Hartl, Ann. Rev. Biochem. 62: 349-384 (1993); Hartl, Nature 381: 571-580 (1996). Further, heat shock proteins have been shown to play an important role in the proper folding and assembly of proteins in the cytosol, endoplasmic reticulum and mitochondria; in view of this function, they are referred to as "molecular chaperones". Frydman et al., Nature 370: 111-117 (1994); Hendrick and Hartl., Ann. Rev. Biochem. 62:349-384 (1993); Hartl., Nature 381:571-580 (1996).
For example, the protein BiP, a member of a class of heat shock proteins referred to as the hsp70 family, has been found to bind to newly synthesized, unfolded .mu. immuno-globulin heavy chain prior to its assembly with light chain in the endoplasmic reticulum. Hendershot et al., J. Cell Biol. 104:761-767 (1987). Another heat shock protein, gp96, is a member of the hsp90 family of stress proteins which localize in the endoplasmic reticulum. Li and Srivastava, EMBO J. 12:3143-3151 (1993); Mazzarella and Green, J. Biol. Chem. 262:8875-8883 (1987). It has been proposed that gp96 may assist in the assembly of multi-subunit proteins in the endoplasmic reticulum. Wiech et al., Nature 358:169-170 (1992).
It has been observed that heat shock proteins prepared from tumors in experimental animals were able to induce immune responses in a tumor-specific manner; that is to say, heat shock protein purified from a particular tumor could induce an immune response in an experimental animal which would inhibit the growth of the same tumor, but not other tumors. Srivastava and Maki, 1991, Curr. Topics Microbiol. 167: 109-123 (1991). The source of the tumor-specific immunogenicity has not been confirmed. Genes encoding heat shock proteins have not been found to exhibit tumor-specific DNA polymorphism. Srivastava and Udono, Curr. Opin. Immunol. 6:728-732 (1994). High resolution gel electrophoresis has indicated that gp96 may be heterogeneous at the molecular level. Feldweg and Srivastava, Int. J. Cancer 63:310-314 (1995). Evidence suggests that the source of heterogeneity may be populations of small peptides adherent to the heat shock protein, which may number in the hundreds. Id. It has been proposed that a wide diversity of peptides adherent to tumor-synthesized heat shock proteins may render such proteins capable of eliciting an immune response in subjects having diverse HLA phenotypes, in contrast to more traditional immunogens which may be somewhat HLA-restricted in their efficacy. Id.
Lukacs et al., J. Exp. Med. 178: 343-348 (1993), have reported the transfection of tumor cells with a mycobacterial heat shock protein-encoding gene, and the observation that the transfected cells lose tumorigenicity and induce what appears to be T-cell mediated protection against tumors in mice immunized using the transfected cells. Lukacs et al. suggest that the loss of tumorigenicity could result from the interaction of the heat shock protein with p53 via increased efficiency of chaperone activity to produce proper folding and conformation of otherwise ineffective p53 protein. They further suggest that the highly immunogenic nature of the 65 kD bacterial hsp enhances the recognition of other, tumor-associated antigen molecules.
It has been suggested in the literature that mycobacterial heat shock proteins may play a role in the onset of autoimmune diseases such a rheumatoid arthritis. Thus, the practical utility of such bacterial proteins in vaccines for the treatment of humans is questionable. It is an object of the present invention to provide vaccine compositions which can be used to stimulate an immune response to antigens, including tumor and infectious disease antigens, present in mammalian cells without the introduction of mycobacterial proteins.